J.H. Yin, H.H. Zhu, and K.W. Fung
The Department of Civil and Structural Engineering, The Hong Kong Polytechnic University Hung Hom,
Kowloon, Hong Kong, China
W. Jin
The Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong, China
L.M. Mak and K. Kuo
LMM Consulting Engineers Ltd, Suite 901, 88 Hing Fat Street, North Point, Hong Kong, China

ABSTRACT
The measurement of displacements occurred within geotechnical structures is of great importance. Existing techniques for measuring displacements inside geotechnical structures have limitations. This paper introduces innovative optical fiber sensors based on fiber Bragg grating (FBG) technology and associated devices for measuring displacements within geotechnical structures, for example, inside a slope or soil ground. The scientific principle of the sensors are
presented and explained first. All optical fiber sensors are designed and made in The Hong Kong Polytechnic University. All sensors have been calibrated in laboratory. Typical calibration results are presented. Afterwards, the optical fiber sensors are used to monitor the internal displacements of a model dam. The results measured using these optical fiber sensors are compared with those obtained using conventional displacement transducers. It is found that the results from the two technologies are in good agreement. The advantages of the optical fiber sensors are presented. The innovative optical fiber sensors have great potential applications in Hong Kong, for example, measuring lateral movement of slopes, heave or settlement of ground due to trenchless tunneling, settlement of soft soil ground, lateral movement of excavations, etc.

YIN, J.-H., ZHU, H.-H., FUNG, K.-W., JIN, W., MAK, L. M., and KUO, K. (2008)."Innovative Optical Fiber Sensors for Monitoring Displacement of Geotechnical Structures." The HKIE Geotechnical Division 28th Annual Seminar, Hong Kong, 287-294.